Nutritional quality of semi-arid grassland in western Spain over a 10- year period: changes in chemical composition of grasses, legumes and forbs.

From 1987 to 1996, nutritional quality of the main botanical components (grasses, legumes and forbs) in semi-arid grasslands in the dehesa ecosystem in western Spain was analysed. Herbage samples were collected at the end of spring season, in 30 locations, at two different topographic positions (upper and lower slope zones). Herbage mass over 2 cm and proportion of botanical components were estimated and samples were analysed for crude protein, neutral-detergent fibre (NDF), hemicellulose, cellulose, lignin and in vitro dry matter digestibility (DMD). Analysis of variance revealed a significant effect of sampling year on the herbage mass, proportion of botanical components and their nutritional quality. The three botanical groups followed similar year-to-year trends in their crude protein, cellulose and lignin contents and in vitro DMD. Herbage mass was not significantly related to any meteorological variables, suggesting that inter-annual variation in biomass production of botanically complex pastures cannot be explained by a single factor. However, annual precipitation was significantly related to the proportion of the botanical group which was dominant at each slope zone: grasses in the lower zone and forbs in the upper zone. In the upper zone spring precipitation explained part of the inter-annual variation in the NDF, cellulose, lignin contents and in vitro DMD of the botanical components.We are grateful to L. García, J.C. Estévez and M. Hernández for practical assistance. This work was financially supported by the Directorate General for Agriculture of the European Union (Contract 8001-CT90-0021) and the Spanish “Comisión Interministerial de Ciencia y Tecnología” (C.I.C.Y.T.; AGF96-0423).Peer reviewe